Mobile communications network, communications device and methods

ABSTRACT

A communications device is configured to transmit and receive data via a wireless access interface provided by a mobile communications network. The wireless access interface provides a plurality of communications resource elements across a host frequency range of a host carrier, and providing a first section of the communications resources within a first frequency range for preferable allocation to reduced capability devices forming a first virtual carrier and, the first frequency range being within the host frequency range, and the wireless access interface includes a plurality of time divided sub-frames, and at least one of the sub-frames includes a control channel in a part of the sub-frame for communicating signaling messages to the communications devices and the reduced capability devices. The mobile communications network transmits first resource allocation messages to the communications devices to allocate one or more of the plurality of communications resource elements of the host frequency range of the host carrier and transmits second resource allocation messages to the reduced capability devices to allocate one or more of the first section of the communications resources within the first frequency range for preferable allocation to the reduced capability devices of the first virtual carrier, the first resource allocation messages identifying one or more of the communications resource of the host carrier allocated to the communications devices with reference to a first reference frequency of the host frequency band and the second resource allocation messages identifying the one or more communications resources of the first virtual carrier allocated to the reduced capability devices with reference to a second reference frequency within the first virtual carrier. As a result the amount of signalling information in the second resource allocation messages which is transmitted to the reduced capability devices to allocate resource in the virtual carrier can be reduced.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates to mobile communications networks andmethods for communicating data using mobile communications networks,infrastructure equipment for mobile communications networks,communications devices for communicating data via mobile communicationsnetworks and methods of communicating via mobile communicationsnetworks.

BACKGROUND OF THF DISCLOSURE

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architecture are able to support more sophisticated services than simplevoice and messaging services offered by previous generations of mobiletelecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. The demand to deploy third and fourth generationnetworks is therefore strong and the coverage area of these networks,i.e. geographic locations where access to the networks is possible, isexpected to increase rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a class of devices andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing ubiquity of the coverage area. Examples include so-calledmachine type communication (MTC) applications, which are typified bysemi-autonomous or autonomous wireless communication devices (i.e. MTCdevices) communicating small amounts of data on a relatively infrequentbasis. Examples include so-called smart meters which, for example, arelocated in a customer's house and periodically transmit information backto a central MTC server data relating to the customers consumption of autility such as gas, water, electricity and so on. Other examplesinclude medical devices which are continuously or intermittentlytransmitting data such as for example measurements or readings frommonitors via a communications network to a server, and automotiveapplications in which measurement data is gathered from sensors on avehicle and transmitted via a mobile communications network to a serverattached to the network.

Whilst it can be convenient for a terminal such as an MTC type terminalto take advantage of the wide coverage area provided by a third orfourth generation mobile telecommunication network, there are at presentdisadvantages and challenges to successful deployment. Unlike aconventional third or fourth generation terminal device such as asmartphone, an MTC-type terminal is preferably relatively simple andinexpensive, having a reduced capability. In addition MTC-devices areoften deployed in situations that do not afford easy access for directmaintenance or replacement, so that reliable and efficient operation canbe crucial. Furthermore, while the type of functions performed by theMTC-type terminal (e.g. collecting and reporting back data) do notrequire particularly complex processing to perform, third and fourthgeneration mobile telecommunication networks typically employ advanceddata modulation techniques (such as 16QAM or 64QAM) on the radiointerface which can require more complex and expensive radiotransceivers to implement.

It is usually justified to include such complex transceivers in asmartphone as a smartphone will typically require a powerful processorto perform typical smartphone type functions. However, as indicatedabove, there is now a desire to use relatively inexpensive and lesscomplex devices to communicate using LTE type networks. In parallel withthis drive to provide network accessibility to devices having differentoperational functionality, e.g. reduced bandwidth operation, there is adesire to optimise the use of the available bandwidth in atelecommunications system supporting such devices. Accordingly it hasbeen proposed to provide a so called “virtual carrier” within the hostcarrier bandwidth of an LTE network, which provides communicationsresources for preferable allocation to MTC-type devices, which arereferred to interchangeably in the following description as VC-UEs. Avirtual carrier is therefore tailored to low capability terminals suchas MTC devices and is thus provided within the transmission resources ofat least the conventional OFDM type downlink carrier (i.e. a “hostcarrier”). Unlike data transmitted on a conventional OFDM type downlinkcarrier, data transmitted on the virtual carrier can be received anddecoded without needing to process the full bandwidth of the downlinkhost OFDM carrier, for at least some part of a sub-frame. Accordingly,data transmitted on the virtual carrier can be received and decodedusing a reduced complexity receiver unit.

The term “virtual carrier” corresponds in essence to a narrowbandcarrier for MTC-type devices within a host carrier for an OFDM-basedradio access technology (such as WiMAX or LTE).

The virtual carrier concept is described in a number of co-pendingpatent applications (including GB 1101970.0 [2], GB 1101981.7 [3], GB1101966.8 [4], GB 1101983.3 [5], GB 1101853.8 [6], GB 1101982.5 [7], GB1101980.9 [8] and GB 1101972.6 [9]), the contents of which areincorporated herein by reference.

In order to deploy a virtual carrier for access by communicationsdevices such as MTC devices some adaptation of existing signalling andmessages may be required, but as far as possible without adapting thehost mobile communications network so as to provide compatibility withconventional communications devices.

SUMMARY OF THE DISCLOSURE

According to a first aspect there is provided a communications devicefor transmitting data to or receiving data from a mobile communicationsnetwork. The communications device may be a reduced capability device(VC-UE) and may form part of an MTC-device or terminal. The mobilecommunications network includes one or more network elements, the one ormore network elements providing a wireless access interface for thecommunications device. The communications device comprises a transmitterunit adapted to transmit signals representing the data to the mobilecommunications network via the wireless access interface provided by theone or more network elements of the mobile communications network, and areceiver unit adapted to receive signals representing the data from themobile communications network via the wireless access interface. Thewireless access interface provides a plurality of communicationsresource elements across a host frequency range of a host carrier, and afirst section of the communications resources within a first frequencyrange for preferable allocation to reduced capability devices forming afirst virtual carrier, the first frequency range being within the hostfrequency range. The wireless access interface includes a plurality oftime divided sub-frames, and at least one of the sub-frames includes acontrol channel in a part of the sub-frame for communicating signalingmessages to the communications devices and the reduced capabilitydevices. The one or more network elements transmit first resourceallocation messages to the communications devices to allocate one ormore of the plurality of communications resource elements of the hostfrequency range of the host carrier and transmit second resourceallocation messages to the reduced capability devices to allocate one ormore of the first section of the communications resources within thefirst frequency range for preferable allocation to the reducedcapability devices of the first virtual carrier. The first resourceallocation messages identify one or more of the communications resourceof the host carrier allocated to the communications devices withreference to a first reference frequency of the host frequency band. Thesecond resource allocation messages identify the one or morecommunications resources of the first virtual carrier allocated to thereduced capability devices with reference to a second referencefrequency within the first virtual carrier. The communications deviceincludes a controller configured to control the receiver unit to receiveone of the second resource allocation message from the control channel,and to receive the data transmitted from the mobile communicationsnetwork via the one or more communications resource allocated by thesecond resource allocation messages with reference to the secondreference frequency within the virtual carrier.

Embodiments of the present technique can provide a more efficientallocation of downlink resources to a communications device which isoperating to receive data from a virtual carrier which is provided by amobile communications network within a host carrier. In order toallocate downlink resources to the communications device which may beoperating as a reduced capability device, such as an MTC type device, aresource allocation message is transmitted on the downlink in a controlchannel. In one example the control channel is the same control channelwhich is transmitting resource allocation messages to conventionalcommunications devices and reduced capability devices. Thus bothconventional communications devices and reduced capability devicesreceive downlink resource allocation messages from the control channel.In the example of LTE the control channel is the PDCCH. One option wouldbe to provide the same downlink resource allocation message for both thereduced capability devices and the conventional communications devices.However, resource allocation messages are arranged to identify resourceswhich are being allocated to a communications device with reference to afrequency within the host frequency band width. For the example ofmobile communications networks operating in accordance with LTEstandards, the reference frequency is the bottom frequency of the hostfrequency band. However according to the present technique a second typeof resource allocation messages are used to allocate resources to reducecapability devices. As such the second resource allocation messages canallocate resources with respect to a reference frequency within thevirtual carrier bandwidth. Since the virtual carrier provides a smalleramount of communications resources than those of the host carrier areduction in the amount of information which must be transmitted inorder to allocate resources to the reduced capability devices can bemade because the indication of the resources allocated from the virtualcarrier can be made with reference to the reference frequency within thevirtual carrier which can correspondingly provide an allocation ofresources using a smaller amount of data than that which would berequired to allocate resources with reference to a frequency within thehost carrier. Accordingly, a more efficient use of communicationsresources can be achieved and a more efficient operation of thecommunications device.

In the following description conventional communications devices will bereferred to as User Equipment (UE's) which is a term which can be usedinterchangeably with communications device, and reduce capabilitydevices will be referred to as a Virtual Carrier-User Equipment (VC UE).Accordingly, the context and differentiation between these types ofdevices should be clarified although this is by way of example andshould not be taken to be limiting.

Various further aspects and features of the present disclosure aredefined in the appended claims and include a communications device, amethod of receiving data using a communications device, a mobilecommunications network, an infrastructure equipment and a method oftransmitting data from a mobile communications network.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure will now be described by way ofexample only with reference to the accompanying drawings wherein likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram illustrating an example of aconventional mobile telecommunication network;

FIG. 2 provides a schematic diagram illustrating a conventional LTEradio frame;

FIG. 3 provides a schematic diagram illustrating an example of aconventional LTE downlink radio sub-frame;

FIG. 4 provides a schematic diagram illustrating an example of an LTEdownlink radio sub-frame in which a narrow band virtual carrier has beeninserted at the centre frequency of the host carrier, the virtualcarrier region abuts the wideband PDCCH control region of the hostcarrier, which is making a characteristic “T-shape”;

FIG. 5 provides a schematic diagram illustrating an example of a LTEdownlink radio sub-frame in which virtual carriers have been inserted ata number of frequencies of the host carrier;

FIG. 6 provides a schematic diagram illustrating the relationshipbetween CCEs and REs within the HC control region;

FIG. 7a is a part schematic block diagram, part flow diagram providing arepresentation of a transmission of a down-link resource allocationmessage of a first example from the eNB of a mobile communicationsnetwork to a conventional communications device (UE); whereas FIG. 7bprovides a corresponding part schematic block diagram part flow diagramproviding a representation of a transmission of a down-link resourceallocation message of a second example from the eNB of a mobilecommunications network to a reduced capability device (VC-UE);

FIG. 8 provides a schematic diagram illustrating a part of a mobilecommunications network adapted to provide radio access to conventionalLTE terminal and reduced capacity terminals (VC-UE) according to thepresent technique; and

FIG. 9 is a flow diagram illustrating a method of allocating down-linkcommunications resources in accordance with the present technique.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Previous co-pending applications have discussed in detail the design andoperation of some parts of a so-called virtual carrier (VC), embedded ina classical host carrier (HC), suitable for use particularly in LTEnetworks serving machine-type communication (MTC) devices among theirmix of user equipment terminals (UEs). One particular version of the VCdesign is a so-called ‘T-shaped’ VC, a fuller description of which maybe found in co-pending patent application number GB 1121767.6 [11]. Astructure for this is illustrated in FIG. 4. In such a VC, the VC-UE isassumed to be able to decode the wideband control region on the HC, butis thereafter confined to relatively narrowband resources for physicaldownlink shared channels (PDSCH), etc. on the VC.

The control region defined in current releases of L′I′E includes thePCFICH, PHICH, PDCCH and reference signals (RS). Of interest here is thephysical downlink control channel (PDCCH). A UE must search through thecontrol region to find two sets of information carried on PDCCH: a firstset that is broadcast to all UEs, and a second set that is intended forthe UE alone. This searching is done by “blindly decoding” all possiblelocations and combinations of resource elements (REs) that could formthe UE's PDCCH, and the channel specifications define how the REs shouldbe combined into PDCCH candidates.

The procedure for searching the possible PDCCH candidates is termed“blind decoding” as no information is provided by the network that wouldallow a more targeted search among the possible PDCCH candidates.

In LTE, the identifier used to direct data to any given UE is known as aRadio Network Temporary Identifier. Depending upon the context within acommunication session, the RNTI may take one of a number of forms. Thusdata that is UE specific uses either a C-RNTI (cell RNTI) or a temporaryC-RNTI; data intended for broadcast of system information uses a SI-RNTI(system information RNTI); paging signals use a P-RNTI (paging RNTI);messages concerning the random access procedure (RA procedure) useRA-RNTI (random access RNTI), etc. The C-RNTI thus uniquely identifies aUE in a cell. RNTIs are assigned from a range of 16-bit values, andspecifications restrict which RNTIs may be taken from which rangeswithin the total possible range. Some values are not permitted for useas any RNTI, referred to in this description as ‘reserved RNTIs’. Incurrent versions of specifications, these are the range FFF4 to FFFCinclusive, in hexadecimal notation.

A UE determines whether a particular PDCCH within the control region isintended for itself by attempting to decode each possible set of REsthat could be a PDCCH, according to the specifications and the eNBconfiguration. In LTE, each RRC-connected UE is assigned a 16-bitC-RNTI, which allows a maximum of about 65000 users to be RRC connected.The assigned C-RNTI (or other UE ID) is used to uniquely address controlinformation to specific UEs in the cell. To reduce signalling overhead,the UE ID will not be sent explicitly. Instead, part of the PDCCH dataintended for the UE is scrambled (masked) with a mask uniquelyassociated with the UE ID by the eNodeB (or other network accessentity). In a particular example, the CRC bits (cyclic redundancychecking bits primarily used in error correction procedures) arescrambled using the C-RNTI.

PDCCH data scrambled with the UE's own C-RNTI may only be de-scrambledwith that same C-RNTI. Thus, in the example, each UE descrambles thereceived CRC bits with its own mask before doing a CRC check.

C-RNTIs are assigned to UEs by the network during the random access (RA)procedure. A similar process is conducted to locate any broadcastinformation, which has CRC scrambled by a common RNTI known to all UEsin the cell, such as the P-RNTI or the SI-RNTI.

Control information is packaged for transmission over the PDCCH instandardised Downlink Control Information (DCI) messages. These DCImessages take different formats depending upon their purpose. DCIformats include: uplink grant signals; downlink shared channel resourceallocation signals; Transmit Power Control (ITC) commands, which adaptthe transmit power of the UE to save power; and MIMO precodinginformation. A more detailed discussion of 3GPP standard DCI formats maybe found in 3GPP TS 36.212 (Section 5.3.3.1) which is incorporatedherein by reference.

Example of an LTE System

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a conventional mobile telecommunications network, usingfor example a 3GPP defined UMTS and/or Long Term Evolution (LTE)architecture.

The network includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices(also referred to as mobile terminals, MT or User equipment, UE) 104.Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplex (OFDM) based interface for theradio downlink (so-called OFDMA) and the radio uplink (so-calledSC-FDMA).

FIG. 2 shows a schematic diagram illustrating an OFDM based L 1Edownlink radio frame 201. The LTE downlink radio frame is transmittedfrom an LTE base station (known as an enhanced Node B) and lasts 10 ms.The downlink radio frame comprises ten sub-frames, each sub-framelasting 1 ms. A primary synchronisation signal (PSS) and a secondarysynchronisation signal (SSS) are transmitted in the first and sixthsub-frames of the LTE radio frame, in frequency division duplex (FDD). Aphysical broadcast channel (PBCH) is transmitted in the first sub-frameof the LTE radio frame. The PSS, SSS and PBCH are discussed in moredetail below.

FIG. 3 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE sub-frame. The sub-framecomprises a predetermined number of “symbols”, which are eachtransmitted over a respective 1/14 ms period. Each symbol comprises apredetermined number of orthogonal sub-carriers distributed across thebandwidth of the downlink radio carrier. Here, the horizontal axisrepresents time while the vertical represents frequency.

The example sub-frame shown in FIG. 3 comprises 14 symbols and 1200sub-carriers spread across a 20 MHz bandwidth, R₃₂₀. The smallestallocation of user data for transmission in LTE is a “resource block”comprising twelve sub-carriers transmitted over one slot (0.5sub-frame). Each individual box in the sub-frame grid in FIG. 3corresponds to twelve sub-carriers transmitted on one symbol.

FIG. 3 shows in hatching resource allocations for four LTE terminals340, 341, 342, 343. For example, the resource allocation 342 for a firstLTE terminal (UE 1) extends over five blocks of twelve sub-carriers(i.e. 60 sub-carriers), the resource allocation 343 for a second LTEterminal (UE2) extends over six blocks of twelve sub-carriers and so on.

Control channel data is transmitted in a control region 300 (indicatedby dotted-shading in FIG. 3) of the sub-frame comprising the first nsymbols of the sub-frame where n can vary between one and three symbolsfor channel bandwidths of 3 MHz or greater and where n can vary betweentwo and four symbols for channel bandwidths of 1.4 MHz. For the sake ofproviding a concrete example, the following description relates to hostcarriers with a channel bandwidth of 3 MHz or greater so the maximumvalue of n will be 3. The data transmitted in the control region 300includes data transmitted on the physical downlink control channel(PDCCH), the physical control format indicator channel (PCFICH) and thephysical HARQ indicator channel (PHICH).

PDCCH contains control data indicating which sub-carriers on whichsymbols of the sub-frame have been allocated to specific LTE terminals.Thus, the PDCCH data transmitted in the control region 300 of thesub-frame shown in FIG. 3 would indicate that UE1 has been allocated theblock of resources identified by reference numeral 342, that UE2 hasbeen allocated the block of resources identified by reference numeral343, and so on.

PCFICH contains control data indicating the size of the control region(typically between one and three symbols, but four symbols beingcontemplated to support 1.4 MHz channel bandwidth).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in the central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 sub-carriers wide (corresponding to a transmissionbandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals thatonce detected allow an LTE terminal device to achieve framesynchronisation and determine the cell identity of the enhanced Node Btransmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that LTE terminals use to properly access the cell. Datatransmitted to individual LTE terminals on the physical downlink sharedchannel (PDSCH) can be transmitted in other resource elements of thesub-frame. Further explanation of these channels is provided below.

FIG. 3 also shows a region of PDSCH 344 containing system informationand extending over a bandwidth of R₃₄₄. A conventional LTE frame willalso include reference signals which are discussed further below but notshown in FIG. 3 in the interests of clarity.

The number of sub-carriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 sub-carriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 3). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesub-carriers across the entire bandwidth of the sub-frame to provide forfrequency diversity. Therefore a conventional LTE terminal must be ableto receive the entire channel bandwidth in order to receive and decodethe control region.

Virtual Carrier

FIG. 4 schematically represents an arbitrary downlink sub-frameaccording to the established LTE standards as discussed above into whichan instance of a virtual carrier 406 has been introduced. The sub-frameis in essence a simplified version of what is represented in FIG. 3.Thus, the sub-frame comprises a control region 400 supporting thePCFICH, PHICH and PDCCH channels as discussed above and a PDSCH region402 for communicating higher-layer data (for example user-plane data andnon-physical layer control-plane signalling) to respective terminaldevices, as well as system information, again as discussed above. Forthe sake of giving a concrete example, the frequency bandwidth (BW) ofthe carrier with which the sub-frame is associated is taken to be 20MHz. Also schematically shown in FIG. 4 by black shading is an examplePDSCH downlink allocation 404. In accordance with the defined standards,and as discussed above, individual terminal devices derive theirspecific downlink allocations 404 for a sub-frame from PDCCH transmittedin the control region 400 of the sub-frame.

By contrast with the conventional LTE arrangement, where a subset of theavailable PDSCH resources anywhere across the full PDSCH bandwidth couldbe allocated to a UE in any given sub-frame, in the T-shaped arrangementillustrated in FIG. 4, VC-UEs maybe allocated PDSCH resources onlywithin a pre-established restricted frequency band 406 corresponding toa virtual carrier.

Accordingly, MTC devices each need only buffer and process a smallfraction of the total PDSCH resources contained in the sub-frame toidentify and extract their own data from that sub-frame.

The example shown in FIG. 4 provides an illustration in which a singlevirtual carrier is formed within a host carrier 406. However, as will beappreciated in any particular cell which is served by a base station 101a wireless access interface provided by the base station may include aplurality of virtual carriers in accordance with a capacity required byreduced capability devices. Such an example of a wireless accessinterface supporting a plurality of virtual carriers is shown in FIG. 5.In FIG. 5 which corresponds substantially to the example shown in FIG. 4and so corresponding parts have the same numerical reference numerals,three virtual carriers are shown 404.1, 404.2, 404.3 within the sharedresources 402 provided by the host carrier. As will be appreciated inthe example shown in FIG. 5 only one of the virtual carriers 404.2 islocated around the centre frequency. Since the other virtual carriers404.1, 404.3 are not located around the central frequency then thesewill not include the various control channels and signals which arelocated around the central region as explained with reference to FIG. 3which are the PSS, SSS and PBCH. The concept of virtual carriersprovided on blocks of OFDM sub-carriers that are not centred on the hostcarrier central frequency is known, for example, from our co-pendingpatent application number GB 113801.3. This describes an arrangementwhere a plurality of reduced capability devices are arranged tocommunicate via virtual carriers which are not located in the centrefrequency of the host carrier. FIG. 5 therefore illustrates an LTEdownlink sub-frame with a plurality of virtual carriers outside of thecontrol region 400. The allocation of multiple virtual carriers hasparticular application when communications devices (UEs) using thevirtual carrier create a significant quantity of traffic at a giventime. It is therefore desirable that the respective subsets of devicesserved by each virtual carrier can locate control signals relevant totheir virtual carrier.

Common and UE Search Spaces for PDCCH

As discussed previously in the context of conventional LTE, at leastsome of the resource elements (REs) comprising a host carrier (HC)control region are predefined to map onto a number of so-called controlchannel elements (CCEs). FIG. 6 illustrates this mapping process in moredetail. In FIG. 6 the information bits comprising the CCEs 602 aresubjected to a process, represented by the steps within a box 604, ofcell-specific bit scrambling, QPSK modulation, an interleaver operatingupon groups of the resulting QPSK symbols, cell-specific shifting of apredetermined number of those QPSK symbols and then the mapping of thosesymbols to REs (the dark shaded slots in the left hand region of thesub-frame structure). Physically, any given CCE is distributed acrossthe REs of the HC control region.

The physical downlink control channel (PDCCH) comprises a number ofCCEs. The number of CCEs comprising a particular PDCCH depends on theaggregation level determined by the eNodeB. A UE must search throughsome number of the CCEs in the control region to determine if there areany that comprise PDCCHs containing control information pertinent to theUE.

The locations of CCEs forming PDCCHs can be arranged by the eNodeB tomake the search process at the UE more efficient by arranging CCEs fordifferent purposes in logical “search spaces”.

Some CCEs are searched (monitored) by all UEs in the cell, these CCEscomprising one or more common search spaces (CSS). The order in whichthe CCEs of the CSSs within each sub-frame are searched by UEs remainsstatic and is given by the specification (i.e. not configured by RRC).

Some CCEs are not searched by all UEs, these CCEs comprising a pluralityof UE-specific search spaces (UESS). The order in which the CCEs of theUESSs for a given UE within each sub-frame are searched is dependentupon the relevant RNTI for that UE: the CCEs with which any one UEbeings searching a UESS will also change between sub-frames within aradio frame.

A CCE may be part of more than one search space. Typically, PDCCHscomprising CCEs in a common search space contain information relevant toall UEs in a cell and PDCCHs comprising CCEs in a UE-specific searchspace contain information relevant only to one UE.

A typical blind decoding process will make around ten attempts to decodecommon search space. The number of attempts may be restricted as the CSSis limited to only certain DCI formats which are explained below (i.e.0, 1A, 3, 3A—see 3GPP TS 36.212), which carry data relevant to all UEsin the cell. Furthermore the size of the CSS is restricted to apredefined number of resource elements (e.g. 144 REs=2 aggregations of8-CCEs or 4 aggregations of 4-CCEs).

By contrast, many more blind decoding attempts (˜30) are typicallyrequired to decode UE-specific search space (UESS) successfully: morepossibilities are available to the eNB in terms of the level ofaggregation applied to UESS (see the discussion of aggregation levelsbelow) and in terms of DCI formats for data directed to specific UEs.

In what follows, unless otherwise indicated or obvious, references to aUE are references to a UE operating on a VC, i.e. a VC-UE.

Transmission of Down-Link Resource Allocation Messages (DLRAM)

As explained above, embodiments of the present technique can provide amore efficient arrangement for transmitting resource allocation messagesto UEs which are communicating using a Virtual Carrier. As explainedabove, DCI messages can provide Down-Link Resource Allocation Message(DLRAM) to allocate communications resources from the shared channel,such as a PDSCH to communications devices (UEs). The DLRAMs aretransmitted to the UEs on a control channel such as the PDCCH and/orEPDCCH. For example in 3GPP specifications for LTE Release 11, EPDCCHcontains only cell-specific DCI messages, but changes may be made by3GPP in the LTE Release 12 or later specifications to extend this toUE-specific DCI messages. In what follows therefore, when a DCI messageis considered generically, this is referred to as transmission on an(E)PDCCH.

As will be appreciated by those familiar with LTE, the resources in asub-frame in which a UE has PDSCH allocated are determined by the eNBscheduler. The allocation of resources are communicated to the UE inpart of a downlink control information (DCI) message on (E)PDCCH asexplained above. However DCI messages contain control information otherthan the resource allocation messages.

There are three different types of downlink resource allocation message(DLRAM).

Type 0

For a Type 0 DLRAM, the host carrier bandwidth is divided into resourceblock groups (RBGs) each comprising a number of contiguous RBs. TheDLRAM is then a simple bitmap indicating which RBGs the UE has PDSCH in.RBGs are used to reduce the size of the bitmap compared to a directbit-per-RB approach, and therefore the size of an RBG increases withhost carrier bandwidth from 1 RB per RBG in 1.4 MHz to 4 RBs per RBG in20 MHz. In effect, for host carrier bandwidths less than 10 RBs, a Type0 DLRAM is a direct bit-per-RB map.

Type 0 DLRAMs can be sent in DCI formats 1, 2, 2A, 2B and 2C for allsystem bandwidths.

Type 1

For a Type 1 DLRAM, the system bandwidth is divided into RBGs on thesame principle as for Type 0. However, the RBGs are further divided intotwo subsets of RBGs, with the subset signalled to the UE in the DLRAM.Within the signalled subset, a bit-per-RB (not bit-per-RBG) bitmap isapplied, together with an indication of whether the bitmap should beinterpreted from the top or the bottom of the RBG subset, meaning thatany individual RB can be indicated, unlike in Type 0. For a given hostcarrier bandwidth, the total size of a Type 0 and a Type 1 DLRAM is thesame.

Type 1 DLRAMs can be sent in DCI formats 1, 2, 2A, 2B and 2C for hostcarrier bandwidths of at least 15 RBs.

Type 2

A Type 2 DLRAM allocates virtual RBs (VRB) in the first place. There areas many VRBs as PRBs across the host carrier bandwidth. The DLRAMindicates a starting VRB and a number of contiguous VRBs that constitutethe resource allocation. There is then a mapping from VRBs to PRBs. Thismapping may be direct, so that a VRB is equivalent to a PRB (termed a‘contiguous’ allocation), or interleaved, acting to scatter the VRBsonto the PRBs (termed a ‘distributed’ allocation).

The indication of the VRB allocation is by signalling a resourceindication value (RIV). If the resource allocation fits wholly into thelower half of the host carrier bandwidth, the RIV is simply:

RIV=N _(RB) ^(DL)(L _(CRBs)−1)+RB_(START).

If the allocation extends into the upper half of the bandwidth, then thecalculation is:

RIV=N _(RB) ^(DL)(N _(RB) ^(DL) −L _(CRBs)+1)+(N _(RB)^(DL)−1−RB_(START)).

N_(RB) ^(DL) is the downlink host carrier bandwidth in VRBs, RB_(START)is the index of the first allocated VRB and L_(CRBs) is the length ofthe allocation in contiguous RBs. There is thus a one-to-one mapping ineach host carrier bandwidth from a RIV to a set of VRBs. (The RIVcalculation can be modified slightly to use fewer bits in DCI format 1Cin 1.4 MHz systems, but this is usually limited to a few specificpurposes).

Type 2 DLRAMs are more compact than Types 0 and 1. For example, in a 20MHz host carrier bandwidth, Types 0 and 1 require 25 bits but Type 2requires only 13 bits. In exchange, Type 2 offers eNB less schedulingflexibility because the VRBs must always be allocated contiguously.

Type 2 DLRAMs can be sent in DCI formats 1A, 1B, 1C and 1D for all hostcarrier bandwidths.

Use of DLRAM Types

For the low-cost/low-complexity VC-UEs according to some examples theDCI formats 2/2A/2B/2C which include fields for MIMO operation may notbe used. Of the format 1 DCI family, 1 and 1A are most relevant since 1Bis for closed-loop precoding (a higher complexity operation), 1C is fora few specific purposes such as broadcast SI messages and paging, and 1Dis for multi-user MIMO.

Of format 1 and 1A, 1A is preferred in this scenario since it enablesthe use of the compact Type 2 DLRAMs. Therefore, some examples may usethe DCI format for transmitting the DLRAM of Type 2.

Example Embodiments

DLRAMs indicate to the UE in which RBs across the host carrier bandwidthit will have PDSCH in the current sub-frame. In the example of a 20 MHzhost carrier bandwidth, the Type 2 DLRAMs for DCI format 1A will contain13 bits, and allow the eNB to allocate any contiguous sets of RBs (amongother options). On the other hand, in a 1.4 MHz host carrier bandwidth,the Type 2 DLRAMs for DCI format 1A will contain only 5 bits.

This presents a technical problem because it is desirable to transmit assmall a (E)PDCCH message as possible to maximise (E)PDCCH capacity in asub-frame. Even though a T-VC UE might only be able to access a 1.4 MHzPDSCH, it must still be sent a much larger DLRAM as if accessing a fullhost carrier bandwidth PDSCH, which may be inefficient operationresulting in wasteful use of (E)PDCCH resources. This problem may beparticularly acute in cases where many MTC devices are active and eachneeds some (E)PDCCH.

The basic principle of having a DLRAM constructed by eNodeB andinterpreted by the UE as for a bandwidth different to the host carrierbandwidth can be applied to transmission of a control message which isdecoded across the host carrier bandwidth, and so is referred to simplyas just a PDCCH.

Unfortunately, it is not a solution to simply send the UE a 1.4MHz-compliant Type 2 DLRAM because it would be interpreted always fromthe lowest-numbered RB in the host carrier bandwidth, not thelowest-numbered RB in the predetermined restricted bandwidth of theT-VC. Similarly, using other DLRAM types as applicable to other hostcarrier bandwidths and DCI formats will face the same basic problem: itis not possible merely to transmit a DLRAM suitable for the restrictedPDSCH bandwidth in order to save (E)PDCCH resources, because such aDLRAM will be interpreted in current specifications according to the LTEhost carrier bandwidth and result in the UE decoding inappropriate RBsfor PDSCH. Therefore, new solutions such as those disclosed below areneeded.

Embodiments of the present technique can provide an arrangement in whicha UE operating on a virtual carrier is configured to interpret DLRAMswith respect only to the predetermined restricted bandwidth, rather thanthe DL host carrier bandwidth; and that the eNB is modified to produceand transmit DLRAMs that can be so interpreted. This therefore has twoprincipal aspects: eNB behaviour and UE behaviour. An illustration of anexample embodiment is shown in FIGS. 7a and 7 b.

As shown in FIG. 7a an eNode-B 701 is arranged to transmit a DLRAM1providing a first format 702 to a communications device or UE 704. TheeNB 701 may form part of, for example, an LTE mobile communicationsnetwork. The DLRAM 1 is transmitted in the PDCCH of the LTE downlink inaccordance with a conventional operation as a DCI message. As shownpictorially in FIG. 7a a simplified representation of the downlinksub-frame structure which is shown in FIG. 3 is presented generally as agraphical representation 710. As shown in FIG. 7a and in correspondencewith the representation of the LTE downlink sub-frame shown in FIG. 3,the downlink sub-frame 710 represented in FIG. 7a includes a controlregion 712 which corresponds to the PDCCH 300 shown in FIG. 3. Alsoshown in FIG. 7a is a virtual carrier region 720 comprising a reservedset of communications resources for allocation to reduced capabilitydevices.

As shown in FIG. 7a the DLRAM1 allocates resources of the downlink PDSCHto the UE 704. As shown in FIG. 7a communications resources which areshown within a hashed box 722 are to be allocated to the UE 704. Asshown in FIG. 7a the allocation message provides an indication of theresources allocated with respect to a reference frequency 724 which isthe bottom most frequency of the host carrier downlink sub frame. Asshown in FIG. 7a the allocation of the communications resources 722 ismade by referencing the reference frequency 724 as a displacement 726and an allocation 728 which is in some form. For example in any of thetype 0, type 1 or type 2 DLRAM messages could be used such as a bit mapto allocate the communications resources 722.

A corresponding diagram in which a DLRAM2 is transmitted to a reducedcapability device (VC-UE) is shown in FIG. 7b . As shown in FIG. 7b anadapted eNB 701 transmits a DLRAM2 of a second type 742 to an MTC typeUE VC-UE 744. As with the conventional arrangement presented in FIG. 7athe DLRAM2 742 is transmitted in the PDCCH 712 of the downlinksub-frame. Again the message provided in the DLRAM2 allocating resourcesto the VC-UE 744 is presented pictorially as a simplified version of thehost carrier bandwidth 710 to represent the information conveyed by theDLRAM 2. As shown in FIG. 7b the DLRAM2 allocates resources withreference to a reference frequency 750 which is within the virtualcarrier region 720. In this example, the reference frequency 750 withinthe virtual carrier 720 is the bottom most frequency of the virtualcarrier. However, in other examples the reference frequency 750 could beany other frequency within the virtual carrier. However, by providingthe reference frequency 750 to be within the virtual carrier 720 then abit map or offset can be used to represent the allocated downlinkresources represented by the DLRAM2 to allocate these resources to theVC-UE 744. Again, as with the example showing in FIG. 7a , theallocation of resources is done with reference to an offset 756 and anallocation of resources 758 which indicates both frequency and time ofthe communications resources allocated to the VC-UE 744. However byusing a bit map such as the messages of type 0 or type 1, or with a type2 format, it can be appreciated that the representation of the allocatedresources can be conveyed to the VC-UE with a smaller amount ofinformation by using the reference frequency 750 within the virtualcarrier 720. Accordingly an efficiency of communication and processingcan be performed and achieved with an eNB 701 and a VC-UE 744 adapted tooperate in this way.

Example Adapted Wireless Communications System

A simplified representation of a mobile communications network adaptedto operate in accordance with the present technique is shown in FIG. 8whilst parts also appearing in FIG. 1 bear the same numerical referencenumerals. As shown in FIG. 8, conventional UEs 104 operate within thecell 103 with VC-UE's 801 to transmit and to receive data via a virtualcarrier formed by an adapted eNB 800. As shown in FIG. 8, theconventional UE's 104 include transceiver units 802 which are controlledby a controller 804.

As explained with reference to FIG. 7a the conventional UE's 104 arearranged to receive the first resource allocation messages DRLAM 1 fromthe eNB 800 to allocate resources within the host carrier. In contrastthe UE's 810 which also include a transceiver unit 812 and a controller814 are adapted to receive the DLRAM 2 messages of a second type asshown in FIG. 7b to allocate resources from within the virtual carrier.As shown in FIG. 8 the adapted eNB 800 includes a controller 820 whichcontrols the transceiver 822 to form the up and downlink of the wirelessaccess interface and provides the virtual carrier at least on thedownlink which is reserved for allocating communications resources tothe VC-UE's 810.

Adapted Infrastructure Equipment (eNB)

As explained above, the eNB 800 determines the contents of the DLRAM2messages of the second example according not to the DL host carrierbandwidth but according instead to the predetermined restricted VCbandwidth configured for the VC-UE of interest. The eNB 800 differencedepends on DLRAM type:

In the case of a Type 0 DLRAM, this amounts to re-mapping the RBG bitmapfrom the host carrier bandwidth to the restricted PDSCH bandwidth, andrestricting the allowed size of the bitmap to the smallest one matchinghost carrier bandwidths larger than the restricted PDSCH bandwidth. Onere-mapping is to truncate from the bitmap all the bits relating to RBGsnumbered lower than the lowest RBG included in the restricted PDSCHbandwidth.

In the case of a Type 1 DLRAM this amounts to the same alterations asfor a Type 0 DLRAM. There is no need for alterations to the RBG subsetindication or to the offset flag. Note, however, the applicabilityconstraints Type 1 DLRAMs given in Section 1. However, Type 1 DLRAMs are(as of Rel-11) only applicable to bandwidths of at least 15 RBs, and canonly be sent in DCI formats 1 and 2/2A/2B/2C, so they may be lessdesirable for use with low-cost/complexity UEs.

In the case of a Type 2 DLRAM, this amounts to altering the RNcalculation. Currently:

RIV=N _(RB) ^(DL)(L _(CRBs)−1)+RB_(START), or

RIV=N _(RB) ^(DL)(N _(RB) ^(DL) −L _(CRBs)+1)+(N _(RB)^(DL)−1−RB_(START)).  (1)

The formula and eNB behaviour changes according to:

RIV=N _(RB) ^(VCDL)(L _(CRBs)−1)+RB_(START)−RB_(START) ^(VC), or

RIV=N _(RB) ^(VCDL)(N _(RB) ^(VCDL) −L _(CRBs)+1)+[N _(RB)^(VCDL)−1−(RB_(START)−RB_(START) ^(VC))]  (2)

respectively, where N_(RB) ^(VCDL) is the number of RBs in the bandwidthof the T-VC for PDSCH (the predetermined restricted bandwidth),RB_(START) ^(VC) is the index in the host carrier of the lowest VRB inthe T-VC for PDSCH, and RB_(START) is still the index in the hostcarrier of the lowest allocated VRB. Alternatively, RB_(START) could bespecified to be determined with respect to the index of the lowest RB inthe restricted PDSCH bandwidth, and RB_(START) not introduced.

Note that these alterations and calculations can be different per-UEaccording to the differing restricted PDSCH bandwidths they may beconfigured with. In current systems, the eNB 800 does not distinguishUEs in this way.

Adapted UE 810

The VC-UE 810 interprets the DLRAM not according to the RBs of the DLhost carrier bandwidth but according only to those RBs which lie withinits T-VC. Note that the UE is ‘aware’ of the host carrier bandwidth asusual: it decodes PDCCH across it, and might in some T-VC cases havePDSCH scheduled in any restricted part of it. However, it alters itsunderstanding of a DLRAM according to its current T-VC configuration,which can change over time.

A more general T-VC UE might have more than one restricted bandwidthwithin which it is expected to decode PDSCH. In that case, there are twosolutions:

(a) The UE might be given more than DLRAM, along with an indicator ine.g. an associated DCI message as to which one of the restrictedbandwidths each applies to, and the UE then interprets each DLRAMindependently and accordingly.

(b) For a Type 2 DLRAM, the UE can be given a DLRAM according toequation (2), and be further operable to ignore those parts of it whichspan RBs which do not lie within any of the UE's restricted PDSCHregions. In that case, RB_(START) ^(VC) (or RB_(START)) would become theindex of the lowest RB of all the restricted PDSCH regions applicable tothe VC-UE, and N_(RB) ^(VCDL) would become the total number of RBsspanning the lowest numbered RB to the highest numbered RB across allthe restricted regions applicable to the UE. For Type 0 and 1 DLRAMs,the eNB methods need not be altered further than already described.

In accordance with the present technique the adapted eNB 800 and theadapted VC-UE's 810 operate in accordance with the present technique aspresented in a flow diagram shown in FIG. 9 which is summarised asfollows:

S1: A wireless access interface provided by a mobile communicationsnetwork is adapted to provide a virtual carrier which effectivelyreserves resources of the host carrier for reduced capability devices.It is therefore assumed that the reduced capability devices (VC-UEs) mayonly be able to decode signals from within the virtual carrier on somechannels although the radio frequency part may be sufficient to receivecontrol channel signals from across the frequency range of the hostcarrier (PDCCH). As such reduced capability devices (VC-UEs) can receivecontrol signals from a conventional PDCCH, for example. Thus the virtualcarrier provides communications resources within a first frequency rangefor preferable allocation to reduced capability devices (VC-UEs).

S2: At a decision point S2 the eNB determines whether it is allocatingresources on the downlink to a conventional UE or a reduced capabilitydevice VC-UE 810.

S4: If the communications resources are being allocated to aconventional UE then a first resource allocation message is transmittedto the UE of a first type (DLRAM 1) which allocates resources within thehost frequency range of the host carrier.

S6: The UE 104 then receives the first DLRAM 1 and identifies theallocated downlink resources of the host carrier using a referencefrequency which is within the host carrier. Thus with the example shownin FIG. 7a , which corresponds to the example of LTE, the referencefrequency is the bottom most frequency of the downlink wireless accessinterface.

S8: In accordance with the conventional operation therefore conventionalUEs 104 then receive data from the resources allocated on the downlinkfor example within the PDSCH of the host carrier.

S10: If the adapted eNB 800 is allocating resources within the virtualcarrier, then the eNB 800 transmits a second resource allocation messageto a VC-UE to allocate one or more of the first section ofcommunications resources within the first frequency range of the firstvirtual carrier. Accordingly, the adapted eNB 800 transmits a downlinkresource allocation message of a second type (DLRAM 2) to the VC-UE 810to allocate one or more of the first section of communications resourceswithin the frequency range of the first virtual carrier. The DLRAM 2message provides a resource allocation of resources with reference to asecond reference frequency, which is within the virtual carrier, therebyreducing the amount of information which must be transmitted torepresent the allocation of resources within the virtual carrier.

S12: The VC-UE 810 then receives the DLRAM 2 message and identifies theresources within the virtual carrier which have been allocated to it forreceiving data on the downlink. The allocation resources may be within aspecific time slot of the sub frame and on a specific frequency withinthe virtual carrier.

S14: The VC-UE 810 then receives the data on the downlink from theallocated resources.

S16. The process then terminates.

Cell-Specific Vs. UE-Specific (E)PDCCHs

As mentioned above, DCI messages can convey DLRAMs which are common tothe cell, i.e. broadcast information on PDSCH such as SI, as well asUE-specific DLRAMs, i.e. PDSCH allocations dedicated to a LTE. A DLRAMfor cell-specific information must therefore be interpretable by allUEs, whether legacy or advanced i.e operable in accordance with thepresent technique, and with all restricted PDSCH bandwidths. Therefore,they must be sent using legacy DLRAM methods. One way of making thisdistinction is to specify that an (E)PDCCH sent in the common searchspace is to use legacy DLRAMs, while the eNB has the option of using there-interpreted DLRAMs of this disclosure if the (E)PDCCH is sent in theUE-specific search space. A UE may receive both types of DLRAM in asub-frame since a common and a UE-specific (E)PDCCH can be sent persub-frame. Alternatively, for the advanced UEs, the restricted PDSCHbandwidth could be re-configured at times when the UE is required toread some broadcast PDSCH so that all such UEs have the same restrictedPDSCH bandwidth.

Multiple Virtual Carriers

As illustrated by the example shown in FIG. 5, embodiments of thepresent technique can include arrangement in which more than one virtualcarrier has been allocated in a cell. Accordingly, VC-UE's may becommunicating via one or more of the virtual carriers 404.1, 404.2,404.3 to which they have been allocated resources. In one example eachof the virtual carriers 404.1, 404.2, 404.3 is provided with a differentDLRAM message so that when VC-UEs receive a DLRAM from the eNB whichconveys the allocation of communications resources with respect to areference frequency from within the virtual carrier. In one example theeNB transmits system information providing the reference frequency whichis allocated to each of the different virtue carriers.

Other Example Embodiments

Embodiments of the present technique can provide an arrangement in whicha reduced amount of information can be used to allocate resources forVC-UEs so that the DLRAMs can be reduced. This can be achieved becausefor example DLRAMs sized for a 1.4 MHz bandwidth can control UEs whichnevertheless are operating in a 20 MHz host carrier bandwidth. This inturn allows smaller DCI messages to be sent on (E)PDCCH, which permitsmore (E)PDCCHs to be sent per sub-frame, reducing latency in the cell,and/or (E)PDCCHs to be sent at higher aggregation levels, improvingdetectability of control information and therefore cell coverage andcell spectral efficiency. At the same time, the UE manufacturer candevelop UEs with low costicomplexity to suit applications such as MTC.

To demonstrate the advantages of the present technique, consider theexample of a 20 MHz host carrier bandwidth:

-   -   The size of a Type 0 DLRAM is reduced from 25 bits to as little        as 6 bits for a 6 RB restricted PDSCH region.    -   The size of a Type 1 DLRAM reduced from 25 bits to as little as        8 bits (although this is limited to restricted PDSCH regions of        at least 15 RBs in 3GPP specifications of Release 11).    -   The size of a Type 2 DLRAM is reduced from 13 bits in DCI format        1A/1B/1D to as little as 5 bits for a 6 RB restricted PDSCH        region. In DCI format 1C the equivalent DLRAM is reduced from 9        bits to 3 bits.

In current systems, a DLRAM is always prepared by the eNB andinterpreted by the UE on the basis of the entire host carrier bandwidth.Embodiments of the present technique therefore remove this constraint,and therefore the eNB can construct DLRAMs relevant to a bandwidthdifferent to the host carrier bandwidth, and the UE is operable to orconfigured to interpret DLRAMs differently. Embodiments also allow theeNB to allocate resources more finely in the restricted PDSCH bandwidthwhen using a Type 0 DLRAM than would be possible if the DLRAM wasconstructed for a larger system bandwidth where the RBG size would belarger.

Furthermore, the construction by the eNB and interpretation by UEs ofDLRAMs can now be different per UE according to the width and frequencylocation of the restricted PDSCH bandwidth each UE is configured to use;the constructions and interpretations can also change over time,particularly to suit efficient use of the radio resources in the celland to provide UEs with sufficient radio resources as their needschange.

Various further aspects and features of the present technique aredefined in the appended claims. The following numbered clauses providefurther example aspects:

1. A communications device for transmitting data to or receiving datafrom a mobile communications network, the mobile communications networkincluding one or more network elements, the one or more network elementsproviding a wireless access interface for the communications device, thecommunications device comprising:

a transmitter unit adapted to transmit signals representing the data tothe mobile communications network via the wireless access interface, and

a receiver unit adapted to receive signals representing the data fromthe mobile communications network via the wireless access interface, thewireless access interface providing a plurality of communicationsresource elements across a host frequency range of a host carrier, andproviding a first section of the communications resources within a firstfrequency range for preferable allocation to reduced capability devicesforming a first virtual carrier and, the first frequency range beingwithin the host frequency range, and the wireless access interfaceincludes

a plurality of time divided sub-frames, and at least one of thesub-frames includes

a control channel in a part of the sub-frame for communicating signalingmessages to the communications devices and the reduced capabilitydevices, wherein the one or more network elements are configured totransmit first resource allocation messages to the communicationsdevices to allocate one or more of the plurality of communicationsresource elements of the host frequency range of the host carrier and totransmit second resource allocation messages to the reduced capabilitydevices to allocate one or more of the first section of thecommunications resources within the first frequency range for preferableallocation to the reduced capability devices of the first virtualcarrier, the first resource allocation messages identifying one or moreof the communications resource elements of the host carrier allocated tothe communications devices with reference to a first reference frequencyof the host frequency band and the second resource allocation messagesidentifying the one or more communications resources of the firstvirtual carrier allocated to the reduced capability devices withreference to a second reference frequency within the first virtualcarrier, and the communications device is a reduced capability deviceand includes a controller configured to control the receiver unit

to receive one of the second resource allocation message from thecontrol channel, and

to receive the data transmitted from the mobile communications networkvia the one or more communications resources allocated by the secondresource allocation messages with reference to the second referencefrequency within the virtual carrier.

2. A communications device according to clause 1, wherein the secondresource allocation messages comprise a smaller amount of data than thefirst resource allocation messages.

3. A communications device according to clause 2, wherein the first orthe second resource allocation messages include bit maps of thecommunications resources allocated.

4. A communications device according to clause 2, wherein the secondresource allocation messages include an indication of the communicationsresources allocated in accordance with a formula:

RIV=N _(RB) ^(VCDL)(L _(CRBs)−1)+RB_(START)−RB_(START) ^(VC), or

RIV=N _(RB) ^(VCDL)(N _(RB) ^(VCDL) −L _(CRBs)+1)+[N _(RB)^(VCDL)−1−(RB_(START)−RB_(START) ^(VC))]

where N_(RB) ^(VCDL) is the number of resource blocks in the bandwidthof the first virtual carrier, RB_(START) ^(VC) is an index in the hostcarrier representing a lowest communications resource elementin thevirtual carrier, RB_(START) is an index in the host carrier representinga lowest allocated communications resource element, and L_(CRBs)represents the number of allocated communications resources.

5. A communications device according to any of clauses 1 to 4, whereinthe mobile communications network is configured to transmit anindication of the frequency range of the first virtual carrier, whichconveys the reference frequency within the first virtual carrier withrespect to which the second resource allocation messages identify thecommunications resources allocated to the reduced capability devices.

6. A communications device according to any of clauses 1 to 4, whereinthe mobile communications network is configured to transmit anindication of the reference frequency within the first virtual carrierwith respect to which the second resource allocation messages identifythe communications resources which are allocated to the reducedcapability devices.

7. A communications device according to any of clauses 1 to 6, whereinthe wireless access interface provides a second section of thecommunications resources within a second frequency range for preferableallocation to reduced capability devices forming a second virtualcarrier and, the second frequency range being within the host frequencyrange and including some communications resources which are different tothe first virtual carrier, and the second resource allocation messagesidentify one or more communications resources of the second virtualcarrier allocated to the reduced capability devices with reference to areference frequency within the second virtual carrier.

8 A communications device according to any of clauses 1 to 6, whereinthe wireless access interface provides a second section of thecommunications resources within a second frequency range for preferableallocation to reduced capability devices forming a second virtualcarrier and the second frequency range being within the host frequencyrange and including some communications resources which are different tothe first virtual carrier, and the mobile communications network isconfigured to transmit third resource allocation messages to the reducedcapability devices to allocate one or more of the second section of thecommunications resources within the second frequency range forpreferable allocation to the reduced capability devices of the secondvirtual carrier, the third resource allocation messages identifying theone or more communications resources of the second virtual carrierallocated to the reduced capability devices with reference to areference frequency within the second virtual carrier, and the reducedcapability device includes a controller configured to control thereceiver unit to receive one of the third resource allocation messagefrom the control channel and to receive the data transmitted from themobile communications network via the allocated one or morecommunications resource allocated by the third resource allocationmessages with reference to the reference frequency within the virtualcarrier.

9. A method of receiving data from a mobile communications network, themobile communications network including one or more network elements,the method comprising

providing, from the one or more network elements, a wireless accessinterface, the wireless access interface providing a plurality ofcommunications resource elements across a host frequency range of a hostcarrier, and providing a first section of the communications resourceswithin a first frequency range for preferable allocation to reducedcapability devices forming a first virtual carrier and, the firstfrequency range being within the host frequency range,

dividing the plurality of the communications resources of the hostfrequency range in time into a plurality of time divided units, at leastone of the units including a control channel in a part of the unit forcommunicating signalling messages to the communications devices and thereduced capability devices,

transmitting from the one or more network elements first resourceallocation messages to the communications devices to allocate one ormore of the plurality of communications resource elements of the hostfrequency range of the host carrier, and

transmitting second resource allocation messages to the reducedcapability devices to allocate one or more of the first section of thecommunications resources within the first frequency range for preferableallocation to the reduced capability devices of the first virtualcarrier, the first resource allocation messages identifying thecommunications resources of the host carrier allocated to thecommunications devices with reference to a first reference frequency ofthe host frequency band and the second resource allocation messagesidentifying the one or more communications resources of the firstvirtual carrier allocated to the reduced capability devices withreference to a second reference frequency within the first virtualcarrier, and

receiving at one of the reduced capability devices one of the secondresource allocation messages from the control channel, and

receiving the data transmitted from the mobile communications networkvia the allocated one or more communications resources allocated by thesecond resource allocation messages with reference to the secondreference frequency within the virtual carrier.

10. An infrastructure equipment for forming part of a mobilecommunications network for transmitting data to or receiving data fromcommunications devices, the infrastructure equipment comprising

a mobile communications network including one or more network elements,the one or more network elements providing a wireless access interfacefor the communications device, the communications device comprising:

a transmitter unit adapted to transmit signals representing the data tothe communications devices via a wireless access interface,

a receiver unit adapted to receive signals representing the data fromthe communications devices via the wireless access interface, and

a controller for controlling the transmitter unit and the receiver unitto form the wireless access interface, the wireless access interfaceproviding a plurality of communications resource elements across a hostfrequency range of a host carrier, and providing a first section of thecommunications resources within a first frequency range for preferableallocation to reduced capability devices forming a first virtual carrierand the first frequency range being within the host frequency range, andthe wireless access interface includes

a plurality of time divided sub-frames, and at least one of thesub-frames includes

a control channel in a part of the sub-frame for communicating signalingmessages to the communications devices and the reduced capabilitydevices, wherein the controller is configured in combination with thetransmitter unit

to transmit first resource allocation messages to the communicationsdevices to allocate one or more of the plurality of communicationsresource elements of the host frequency range of the host carrier, and

to transmit second resource allocation messages to the reducedcapability devices to allocate one or more of the first section of thecommunications resources within the first frequency range for preferableallocation to the reduced capability devices of the first virtualcarrier, the first resource allocation messages identifying one or moreof the communications resource of the host carrier allocated to thecommunications devices with reference to a first reference frequency ofthe host frequency band and the second resource allocation messagesidentifying the one or more communications resources of the firstvirtual carrier allocated to the reduced capability devices withreference to a second reference frequency within the first virtualcarrier.

REFERENCES

-   [1] ETSI TS 122 368 V10.530 (2011-07)/3GPP TS 22.368 version 10.5.0    Release 10)-   [2] UK patent application GB 1101970.0-   [3] UK patent application GB 1101981.7-   [4] UK patent application GB 1101966.8-   [5] UK patent application GB 1101983.3-   [6] UK patent application GB 1101853.8-   [7] UK patent application GB 1101982.5-   [8] UK patent application GB 1101980.9-   [9] UK patent application GB 1101972.6-   [10] UK patent application GB 1113801.3-   [11] UK patent application GB 1121767.6

1. A communications device for transmitting data to or receiving datafrom a mobile communications network, the mobile communications networkincluding one or more network elements, the one or more network elementsproviding a wireless access interface for the communications device, thecommunications device comprising: a transmitter unit adapted to transmitsignals representing the data to the mobile communications network viathe wireless access interface, and a receiver unit adapted to receivesignals representing the data from the mobile communications network viathe wireless access interface, the wireless access interface providing aplurality of communications resource elements across a host frequencyrange of a host carrier, and providing a first section of thecommunications resources within a first frequency range for preferableallocation to reduced capability devices forming a first virtual carrierand, the first frequency range being within the host frequency range,and the wireless access interface includes a plurality of time dividedsub-frames, and at least one of the sub-frames includes a controlchannel in a part of the sub-frame for communicating signaling messagesto the communications devices and the reduced capability devices,wherein the one or more network elements are configured to transmitfirst resource allocation messages to the communications devices toallocate one or more of the plurality of communications resourceelements of the host frequency range of the host carrier and to transmitsecond resource allocation messages to the reduced capability devices toallocate one or more of the first section of the communicationsresources within the first frequency range for preferable allocation tothe reduced capability devices of the first virtual carrier, the firstresource allocation messages identifying one or more of thecommunications resource elements of the host carrier allocated to thecommunications devices with reference to a first reference frequency ofthe host frequency band and the second resource allocation messagesidentifying the one or more communications resources of the firstvirtual carrier allocated to the reduced capability devices withreference to a second reference frequency within the first virtualcarrier, and the communications device is a reduced capability deviceand includes a controller configured to control the receiver unit toreceive one of the second resource allocation message from the controlchannel, and to receive the data transmitted from the mobilecommunications network via the one or more communications resourcesallocated by the second resource allocation messages with reference tothe second reference frequency within the virtual carrier.
 2. Acommunications device as claimed in claim 1, wherein the second resourceallocation messages comprise a smaller amount of data than the firstresource allocation messages.
 3. A communications device as claimed inclaim 2, wherein the first or the second resource allocation messagesinclude bit maps of the communications resources allocated.
 4. Acommunications device as claimed in claim 2, wherein the second resourceallocation messages include an indication of the communicationsresources allocated in accordance with a formula:RIV=N _(RB) ^(VCDL)(L _(CRBs)−1)+RB_(START)−RB_(START) ^(VC), orRIV=N _(RB) ^(VCDL)(N _(RB) ^(VCDL) −L _(CRBs)+1)+[N _(RB)^(VCDL)−1+(RB_(START)−RB_(START) ^(VC))] where N_(RB) ^(VCDL) is thenumber of resource blocks in the bandwidth of the first virtual carrier,RB_(START) ^(VC) is an index in the host carrier representing a lowestcommunications resource elementin the virtual carrier, RB_(START) is anindex in the host carrier representing a lowest allocated communicationsresource element, and L_(CRBs) represents the number of allocatedcommunications resources.
 5. A communications device as claimed in claim1, wherein the mobile communications network is configured to transmitan indication of the frequency range of the first virtual carrier, whichconveys the reference frequency within the first virtual carrier withrespect to which the second resource allocation messages identify thecommunications resources allocated to the reduced capability devices. 6.A communications device as claimed in claim 1, wherein the mobilecommunications network is configured to transmit an indication of thereference frequency within the first virtual carrier with respect towhich the second resource allocation messages identify thecommunications resources which are allocated to the reduced capabilitydevices.
 7. A communications device as claimed in claim 1, wherein thewireless access interface provides a second section of thecommunications resources within a second frequency range for preferableallocation to reduced capability devices forming a second virtualcarrier and, the second frequency range being within the host frequencyrange and including some communications resources which are different tothe first virtual carrier, and the second resource allocation messagesidentify one or more communications resources of the second virtualcarrier allocated to the reduced capability devices with reference to areference frequency within the second virtual carrier.
 8. Acommunications device as claimed in claim 1, wherein the wireless accessinterface provides a second section of the communications resourceswithin a second frequency range for preferable allocation to reducedcapability devices forming a second virtual carrier and, the secondfrequency range being within the host frequency range and including somecommunications resources which are different to the first virtualcarrier, and the mobile communications network is configured to transmitthird resource allocation messages to the reduced capability devices toallocate one or more of the second section of the communicationsresources within the second frequency range for preferable allocation tothe reduced capability devices of the second virtual carrier, the thirdresource allocation messages identifying the one or more communicationsresources of the second virtual carrier allocated to the reducedcapability devices with reference to a reference frequency within thesecond virtual carrier, and the reduced capability device includes acontroller configured to control the receiver unit to receive one of thethird resource allocation message from the control channel and toreceive the data transmitted from the mobile communications network viathe allocated one or more communications resource allocated by the thirdresource allocation messages with reference to the reference frequencywithin the virtual carrier.
 9. A method of receiving data from a mobilecommunications network, the mobile communications network including oneor more network elements, the method comprising providing, from the oneor more network elements, a wireless access interface, the wirelessaccess interface providing a plurality of communications resourceelements across a host frequency range of a host carrier, and providinga first section of the communications resources within a first frequencyrange for preferable allocation to reduced capability devices forming afirst virtual carrier and, the first frequency range being within thehost frequency range, dividing the plurality of the communicationsresources of the host frequency range in time into a plurality of timedivided units, at least one of the units including a control channel ina part of the unit for communicating signalling messages to thecommunications devices and the reduced capability devices, transmittingfrom the one or more network elements first resource allocation messagesto the communications devices to allocate one or more of the pluralityof communications resource elements of the host frequency range of thehost carrier, and transmitting second resource allocation messages tothe reduced capability devices to allocate one or more of the firstsection of the communications resources within the first frequency rangefor preferable allocation to the reduced capability devices of the firstvirtual carrier, the first resource allocation messages identifying thecommunications resources of the host carrier allocated to thecommunications devices with reference to a first reference frequency ofthe host frequency band and the second resource allocation messagesidentifying the one or more communications resources of the firstvirtual carrier allocated to the reduced capability devices withreference to a second reference frequency within the first virtualcarrier, and receiving at one of the reduced capability devices one ofthe second resource allocation messages from the control channel, andreceiving the data transmitted from the mobile communications networkvia the allocated one or more communications resources allocated by thesecond resource allocation messages with reference to the secondreference frequency within the virtual carrier.
 10. An infrastructureequipment for forming part of a mobile communications network fortransmitting data to or receiving data from communications devices, theinfrastructure equipment comprising a mobile communications networkincluding one or more network elements, the one or more network elementsproviding a wireless access interface for the communications device, thecommunications device comprising: a transmitter unit adapted to transmitsignals representing the data to the communications devices via awireless access interface, a receiver unit adapted to receive signalsrepresenting the data from the communications devices via the wirelessaccess interface, and a controller for controlling the transmitter unitand the receiver unit to form the wireless access interface, thewireless access interface providing a plurality of communicationsresource elements across a host frequency range of a host carrier, andproviding a first section of the communications resources within a firstfrequency range for preferable allocation to reduced capability devicesforming a first virtual carrier and the first frequency range beingwithin the host frequency range, and the wireless access interfaceincludes a plurality of time divided sub-frames, and at least one of thesub-frames includes a control channel in a part of the sub-frame forcommunicating signaling messages to the communications devices and thereduced capability devices, wherein the controller is configured incombination with the transmitter unit to transmit first resourceallocation messages to the communications devices to allocate one ormore of the plurality of communications resource elements of the hostfrequency range of the host carrier, and to transmit second resourceallocation messages to the reduced capability devices to allocate one ormore of the first section of the communications resources within thefirst frequency range for preferable allocation to the reducedcapability devices of the first virtual carrier, the first resourceallocation messages identifying one or more of the communicationsresource of the host carrier allocated to the communications deviceswith reference to a first reference frequency of the host frequency bandand the second resource allocation messages identifying the one or morecommunications resources of the first virtual carrier allocated to thereduced capability devices with reference to a second referencefrequency within the first virtual carrier.